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Abstract:

Systems and methods are disclosed for improving throughput in a wireless
system utilizing Hybrid Automatic Repeat Request (HARQ) retransmission.
In general, prior to a HARQ-enabled transmission, one or more channel
conditions for a corresponding transmit channel are obtained. Based on
the one or more channel conditions, a set of target block error rates for
the HARQ-enabled transmission are determined. In one embodiment, the set
of target block error rates maximize throughput for the transmit channel
utilizing HARQ retransmission. In another embodiment, the set of target
block error rates optimize throughput and one or more additional
parameters for the transmit channel utilizing HARQ retransmission.

Claims:

1. A method for improving throughput in a wireless system utilizing
Hybrid Automatic Repeat Request, HARQ, retransmission, comprising:
obtaining one or more channel conditions for a transmit channel prior to
a HARQ-enabled transmission; and determining a set of target block error
rates for the HARQ-enabled transmission based on the one or more channel
conditions.

2. The method of claim 1 wherein the set of target block error rates
provides maximum throughput for the transmit channel for the one or more
channel conditions utilizing HARQ retransmission.

3. The method of claim 1 wherein the set of target block error rates
optimizes throughput and one or more additional parameters for the
transmit channel for the one or more channel conditions utilizing HARQ
retransmission.

4. The method of claim 3 wherein the one or more additional parameters
comprise latency.

5. The method of claim 1 wherein the set of target block error rates
includes a separate target block error rate for each transmission
iteration for the HARQ-enabled transmission up to at least a target
transmission iteration for successful reception of the HARQ-enabled
transmission.

6. The method of claim 5 wherein the target transmission iteration is an
N-th transmission iteration for the HARQ-enabled transmission where N is
≧2.

7. The method of claim 6 wherein the set of target block error rates
targets successful reception of the HARQ-enabled transmission on the
target transmission iteration.

8. The method of claim 7 wherein the target transmission iteration
maximizes throughput for the transmit channel for the one or more channel
conditions.

9. The method of claim 7 wherein the target transmission iteration
optimizes throughput and one or more additional parameters for the
transmit channel for the one or more channel conditions.

10. The method of claim 9 wherein the one or more additional parameters
comprise latency.

11. The method of claim 1 wherein a target block error rate from the set
of target block error rates for an i-th transmission iteration of the
HARQ-enabled transmission is greater than or equal to a target block
error rate from the set of target block error rates for an i+1th
transmission iteration of the HARQ-enabled transmission.

12. The method of claim 1 further comprising, for each transmission
iteration for the HARQ-enabled transmission: obtaining a modulation and
coding scheme selected for the transmission iteration of the HARQ-enabled
transmission; and adjusting the modulation and coding scheme for the
transmission iteration based on a target block error rate for the
transmission iteration included in the set of target block error rates to
provide an adjusted modulation and coding scheme for the transmission
iteration.

13. The method of claim 12 wherein, for at least one transmission
iteration of the HARQ-enabled transmission, adjusting the modulation and
coding scheme comprises changing the modulation and coding scheme to a
more aggressive modulation and coding scheme.

14. The method of claim 12 wherein the adjusted modulation and coding
scheme for an i-th transmission iteration of the HARQ-enabled
transmission is at least as aggressive as the adjusted modulation and
coding scheme for an i-1th transmission iteration of the HARQ-enabled
transmission.

15. The method of claim 1 further comprising: obtaining a modulation and
coding scheme selected for a first transmission iteration for the
HARQ-enabled transmission; adjusting the modulation and coding scheme for
the first transmission iteration based on a target block error rate for
the first transmission iteration included in the set of target block
error rates to provide an adjusted modulation and coding scheme for the
first transmission iteration; and for each additional transmission
iteration for the HARQ-enabled transmission: updating the one or more
channel conditions for the transmit channel prior to the additional
transmission iteration to provide one or more updated channel conditions;
determining a new set of target block error rates for the HARQ-enabled
transmission based on the one or more updated channel conditions;
obtaining a modulation and coding scheme selected for the additional
transmission iteration for the HARQ-enabled transmission; and adjusting
the modulation and coding scheme for the additional transmission
iteration based on a target block error rate for the transmission
iteration included in the new set of target block error rates to provide
an adjusted modulation and coding scheme for the additional transmission
iteration.

16. The method of claim 1 further comprising updating the set of target
block error rates prior to each retransmission for the HARQ-enabled
transmission based on the one or more channel conditions.

17. The method of claim 1 further comprising determining a target
transmission iteration for successful reception of the HARQ-enabled
transmission that maximizes throughput.

18. The method of claim 1 further comprising determining a target
transmission iteration for successful reception of the HARQ-enabled
transmission that optimizes throughput and one or more additional
parameters.

19. The method of claim 18 wherein the one or more additional parameters
comprise latency.

20. The method of claim 1 wherein the one or more channel conditions
comprise at least one of a group consisting of: Signal-to-Noise Ratio,
Signal-Interference-to-Noise Ratio, Received Strength of Signal, Bit
Error Rate, a Channel Quality Indicator, and mobile station velocity.

21. The method of claim 1 further comprising: determining whether the
HARQ-enabled transmission is time sensitive; wherein determining the set
of target block error rates comprises: determining the set of target
block error rates for the HARQ-enabled transmission based on the one or
more channel conditions such that the set of target block error rates
optimizes throughput for the transmit channel for the one or more channel
conditions utilizing HARQ retransmission if the HARQ-enabled transmission
is not time sensitive; and determining the set of target block error
rates for the HARQ-enabled transmission based on the one or more channel
conditions such that the set of target block error rates optimizes
latency for the transmit channel for the one or more channel conditions
if the HARQ-enabled transmission is not time sensitive.

22. The method of claim 1 wherein the method is a method of operation of
a base station in the wireless system.

23. The method of claim 22 wherein the wireless system is one of a group
consisting of: a wireless system operating according to the Long Term
Evolution standard, a wireless system operating according to the WiMAX
standard, or a wireless system operating according to the CDMA EVO
standard.

24. A base station in a wireless system that improves throughput
utilizing Hybrid Automatic Repeat Request, HARQ, retransmission,
comprising: a transceiver subsystem; and a processing subsystem
associated with the transceiver subsystem and adapted to: obtain one or
more channel conditions for a transmit channel prior to a HARQ-enabled
transmission; and determining a set of target block error rates for the
HARQ-enabled transmission based on the one or more channel conditions.

25. The base station of claim 24 wherein the transmit channel is an
uplink channel from a mobile station to the base station.

26. The base station of claim 24 wherein the transmit channel is a
downlink channel from the base station to a mobile station.

27. A method for improving throughput in a wireless system utilizing
Hybrid Automatic Repeat Request, HARQ, retransmission, comprising:
controlling a modulation and coding scheme for each transmission
iteration of a plurality of transmission iterations for a HARQ-enabled
transmission based on a target block error rate; and controlling the
target block error rate based on one or more channel conditions for a
transmit channel for the HARQ-enabled transmission.

28. The method of claim 27 wherein controlling the target block error
rate comprises controlling the target block error rate such that
throughput for the transmit channel is maximized for the one or more
channel conditions utilizing HARQ retransmission.

29. The method of claim 27 wherein controlling the target block error
rate comprises controlling the target block error rate such that
throughput and one or more additional parameters for the transmit channel
are optimized for the one or more channel conditions utilizing HARQ
retransmission.

30. The method of claim 27 wherein controlling the target block error
rate based on the one or more channel conditions for the transmit channel
for the HARQ-enabled transmission comprises controlling the target block
error rate to target an N-th transmission iteration for the HARQ-enabled
transmission, where N is ≧2.

31. The method of claim 27 wherein controlling the target block error
rate based on the one or more channel conditions for the transmit channel
for the HARQ-enabled transmission comprises controlling the target block
error rate to target an N-th transmission iteration for the HARQ-enabled
transmission that maximizes throughput for the transmit channel for the
one or more channel conditions utilizing HARQ retransmission, where N is
≧2.

32. The method of claim 27 wherein controlling the target block error
rate based on the one or more channel conditions for the transmit channel
for the HARQ-enabled transmission comprises controlling the target block
error rate to target an N-th transmission iteration of the HARQ-enabled
transmission that optimizes throughput and one or more additional
parameters for the transmit channel for the one or more channel
conditions utilizing HARQ retransmission, where N is ≧2.

33. The method of claim 27 wherein controlling the modulation and coding
scheme comprises controlling the modulation and coding scheme for each
transmission iteration for the plurality of transmission iterations of
the HARQ-enabled transmission based on the target block error rate such
that the modulation and coding scheme for an i-th transmission iteration
is at least as aggressive as the modulation and coding scheme for an
i-1th transmission iteration.

34. A base station in a wireless system that improves throughput
utilizing Hybrid Automatic Repeat Request, HARQ, retransmission,
comprising: a transceiver subsystem; and a processing subsystem
associated with the transceiver subsystem and adapted to: control a
modulation and coding scheme for each transmission iteration of a
plurality of transmission iterations of a HARQ-enabled transmission based
on a target block error rate; and control the target block error rate
based on one or more channel conditions for a transmit channel for the
HARQ-enabled transmission.

35. The base station of claim 34 wherein the transmit channel is an
uplink channel from a mobile station to the base station.

36. The base station of claim 34 wherein the transmit channel is a
downlink channel from the base station to a mobile station.

[0002] Hybrid Automatic Repeat Request (HARQ) is commonly used in modern
communications systems on top of the physic layer in order to mitigate
errors that occur during transmission of data. For instance, the High
Speed Downlink Packet Access for Wideband Code Division Multiple Access
(WCDMA) and Long Term Evolution (LTE) networks use HARQ at the physical
layer to mitigate errors that occur during transmission of data. In
general, in HARQ systems, an incorrectly received data block (e.g., a
packet) is retransmitted and all transmissions for the data block are
jointly decoded. More specifically, in a HARQ system, a transmitter sends
a transmission of data to a receiver. If the receiver is unable to
successfully decode the transmission, the receiver sends a negative
acknowledgement (NACK) to the transmitter over a reverse control channel.
In response, the transmitter performs a HARQ retransmission. For type-I
HARQ, which is sometimes referred to as Chase Combining (CC), the
retransmission comprises the same bits sent in the initial transmission.
For type-II HARQ, sometimes referred to as HARQ with incremental
redundancy, new bits are added to the retransmission. This process is
repeated until the receiver has successfully decoded the transmission or
a maximum allowable number of retransmissions have been performed.

[0003] Traditionally, HARQ systems are configured such that most
HARQ-enabled transmissions are successfully decoded by the receiver on
the first transmission iteration without any retransmissions. The
inventors have found that always targeting successful reception of
HARQ-enabled transmissions on the first transmission iteration does not
utilize the full capacity of the HARQ feature particularly under certain
channel conditions. As such, the present disclosure relates to systems
and methods that utilize HARQ retransmissions to improve throughput in
wireless systems.

SUMMARY

[0004] Systems and methods are disclosed for improving throughput in a
wireless system utilizing Hybrid Automatic Repeat Request (HARQ)
retransmission. In general, prior to a HARQ-enabled transmission, one or
more channel conditions for a corresponding transmit channel are
obtained. The transmit channel may be either an uplink channel or a
downlink channel. Based on the one or more channel conditions, a set of
target block error rates for the HARQ-enabled transmission are
determined. The set of target block error rates are then utilized for the
HARQ-enabled transmission. In one embodiment, the set of target block
error rates maximize throughput for the transmit channel utilizing HARQ
retransmission. In another embodiment, the set of target block error
rates optimize throughput and one or more additional parameters for the
transmit channel utilizing HARQ retransmission. Further, in one
embodiment, the set of target block error rates is static throughout the
HARQ-enabled transmission. In another embodiment, the set of target block
error rates is updated prior to each transmission iteration in the
HARQ-enabled transmission to reflect changes in the one or more channel
conditions for the transmit channel.

[0005] Those skilled in the art will appreciate the scope of the present
disclosure and realize additional aspects thereof after reading the
following detailed description of the preferred embodiments in
association with the accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0006] The accompanying drawing figures incorporated in and forming a part
of this specification illustrate several aspects of the disclosure, and
together with the description serve to explain the principles of the
disclosure.

[0007] FIG. 1 illustrates a base station and a mobile station in a
wireless communication system according to one embodiment of the present
disclosure;

[0008]FIG. 2 is a block diagram that illustrates the operation of the
adaptive block error rate (BLER) and link adaptation functions of FIG. 1
in more detail according to one embodiment of the present disclosure;

[0009] FIGS. 3A and 3B are flow charts that illustrate the operation of
the adaptive BLER function and the outer loop link adaptation function,
respectively, according to one embodiment of the present disclosure;

[0010] FIG. 4 is a flow chart that illustrates the operation of the
adaptive BLER function according to another embodiment of the present
disclosure;

[0011] FIGS. 5A and 5B are flow charts that illustrate the operation of
the adaptive BLER function and the outer loop link adaptation function,
respectively, according to one embodiment of the present disclosure;

[0012] FIG. 6 is a flow chart that illustrates the operation of the
adaptive BLER function according to another embodiment of the present
disclosure;

[0013] FIG. 7 is a graph of exemplary simulation results that illustrate
that always targeting the first transmission iteration does not utilize
the full capacity of a Hybrid Automatic Repeat Request (HARQ) feature;

[0014] FIG. 8 is a graph of simulation results that illustrate that
increasing the target BLER increases throughput for an exemplary transmit
channel;

[0015]FIG. 9 is a graph of exemplary simulation results comparing
throughput for one embodiment of an adaptive target BLER scheme to
throughput for a fixed BLER;

[0018] FIG. 12 is a graph of an exemplary simulation of normalized
throughput versus normalized SNR for a Fixed Modulation and Coding Scheme
(FMC) for HARQ-enabled transmissions;

[0019]FIG. 13 is a graph of an exemplary simulation of normalized
throughput versus normalized SNR for a number of FMCs for HARQ-enabled
transmissions;

[0020] FIG. 14 is a graph that illustrates simulations for normalized
throughput versus normalized SNR for link adaptation with an adaptive
Modulation and Coding Scheme (MCS) for a number of target transmission
iterations; and

[0021] FIG. 15 is a graph similar to that of FIG. 14 that illustrates that
throughput can be improved by targeting different transmission iterations
for different SNR ranges according to one exemplary embodiment of the
present disclosure.

DETAILED DESCRIPTION

[0022] The embodiments set forth below represent the necessary information
to enable those skilled in the art to practice the embodiments and
illustrate the best mode of practicing the embodiments. Upon reading the
following description in light of the accompanying drawing figures, those
skilled in the art will understand the concepts of the disclosure and
will recognize applications of these concepts not particularly addressed
herein. It should be understood that these concepts and applications fall
within the scope of the disclosure and the accompanying claims.

[0023] FIG. 1 illustrates a wireless system 10 according to one embodiment
of the present disclosure. The wireless system 10 may be, for example, a
Long Term Evolution (LTE) wireless system, a WiMAX wireless system, or a
Code Division Multiple Access (CDMA) system. Note, however, that the
wireless system 10 is not limited thereto and may generally be any
wireless system having a Hybrid Automatic Repeat Request (HARQ) feature.
The wireless system 10 includes a base station 12 and a mobile station
14. While FIG. 1 illustrates only one base station 12 and one mobile
station 14, it will be readily appreciated that the wireless system 10
generally includes numerous base stations 12 each serving numerous mobile
stations 14 located within corresponding service areas (e.g., cells) in
the wireless system 10. The base station 12 may be, for example, a LTE
evolved Node B (eNB), but is not limited thereto. In general, the base
station 12 transmits signals to and receives signals from mobile
stations, such as the mobile station 14, within a service area (e.g., a
cell) of the base station 12.

[0024] The base station 12 includes a transceiver subsystem 16 and a
processing subsystem 18. The transceiver subsystem 16 generally includes
analog and, in some embodiments, digital components for sending and
receiving data to and from the mobile station 14. From a wireless
communications protocol view, the transceiver subsystem 16 implements at
least part of Layer 1 (i.e., the Physical or "PHY" Layer). The processing
subsystem 18 generally implements any remaining portion of Layer 1 as
well as functions for higher layers in the wireless communications
protocol for the wireless system 10 (e.g., Layer 2 (data link layer),
Layer 3 (network layer), etc.). Of course, the detailed operation for
each of the functional protocol layers, and thus the transceiver
subsystem 16 and the processing subsystem 18, will vary depending on both
the particular implementation as well as the standard or standards
supported by the base station 12.

[0025] The processing subsystem 18 includes an adaptive block error rate
(BLER) function 20 and a link adaptation function 22. As discussed below
in detail, the adaptive BLER function 20 generally operates to control a
target BLER provided to the link adaptation function 22 for HARQ-enabled
transmissions. For a particular HARQ-enabled transmission, the adaptive
BLER function 20 controls the target BLER for the HARQ-transmission such
that throughput for a corresponding uplink or downlink transmit channel
is improved by utilizing HARQ retransmission. In one embodiment, the link
adaptation function 22 controls a Modulation and Coding Scheme (MCS) for
each transmission iteration of the HARQ-enabled transmission directly or
indirectly based on a corresponding target BLER provided by the adaptive
BLER function 20.

[0026] More specifically, in conventional systems, the target block error
rate utilized by the link adaptation function 22 is a low, static value
(e.g., 10%) such that successful reception of HARQ-enabled transmissions
is always targeted for a first transmission iteration for the
HARQ-enabled transmission (i.e., target zero retransmissions) regardless
of channel conditions. However, the inventors have found that doing so
fails to utilize or exploit the full capacity of HARQ retransmission. In
order to utilize the full capacity, or at least more of the full
capacity, of HARQ retransmission, the adaptive BLER function 20 operates
to control the target block error rate for a HARQ-enabled transmission to
target successful reception on an N-th transmission iteration for the
HARQ-enabled transmission (i.e., the N-1th retransmission) for one or
more channel conditions of a corresponding transmit channel but using a
higher, or more aggressive, MCS. By targeting the N-th transmission
iteration and using a higher MCS, the throughput of the transmit channel
is improved. In one embodiment, the adaptive BLER function 20 controls
the target BLER such that throughput of the transmit channel is maximized
for one or more channel conditions. In another embodiment, the adaptive
BLER function 20 controls the target BLER such that throughput and one or
more additional parameters are optimized for one or more channel
conditions. The one or more additional parameters may be, for example,
latency, Quality of Service (QoS), or the like.

[0027] Those skilled in the art will appreciate that the block diagram of
the base station 12 in FIG. 1 necessarily omits numerous features that
are not necessary to a complete understanding of this disclosure. For
instance, although all of the details of the processing subsystem 18 are
not illustrated, those skilled in the art will recognize that the
processing subsystem 18 comprises one or several general-purpose or
special-purpose microprocessors or other microcontrollers programmed with
suitable software and/or firmware to carry out some or all of the
functionality of the processing subsystem 18 described herein. In
addition or alternatively, the processing subsystem 18 may comprise
various digital hardware blocks (e.g., one or more Application Specific
Integrated Circuits (ASICs), one or more off-the-shelf digital and analog
hardware components, or a combination thereof) configured to carry out
some or all of the functionality of the processing subsystem 18 described
herein.

[0028] The mobile station 14 includes a transceiver subsystem 24 and a
processing subsystem 26. The transceiver subsystem 24 generally includes
analog and, in some embodiments, digital components for sending and
receiving data to and from the base station 12. From a wireless
communications protocol view, the transceiver subsystem 24 implements at
least part of Layer 1 (i.e., the Physical or "PHY" Layer). The processing
subsystem 26 generally implements any remaining portion of Layer 1 as
well as functions for higher layers in the wireless communications
protocol for the wireless system 10 (e.g., Layer 2 (data link layer),
Layer 3 (network layer), etc.). Each of these functional layers may be
implemented in the processing subsystem 26 by means of one or more
microprocessors or microcontrollers executing program code, or by using
one or more appropriately configured hardware blocks, or with some
combination thereof. Of course, the detailed operation for each of the
functional protocol layers, and thus the transceiver subsystem 24 and the
processing subsystem 26, will vary depending on both the particular
implementation as well as the standard or standards supported by the
mobile station 14.

[0029]FIG. 2 is a block diagram illustrating the operation of the
adaptive BLER function 20 and the link adaptation function 22 of FIG. 1
in more detail according to one embodiment of the present disclosure. The
following description for the adaptive BLER function 20 and the link
adaptation function 22 is for a single HARQ-enabled transmission, but it
should be appreciated that this description is applicable to any number
of HARQ-enabled transmissions. In operation, prior to a HARQ-enabled
transmission (i.e., prior to a first transmission iteration for a
HARQ-enabled transmission), the adaptive BLER function 20 obtains one or
more channel conditions for a transmit channel for the HARQ-enabled
transmission. The one or more channel conditions are generally any
parameter that describes the transmit channel such as, for example,
Signal-to-Noise Ratio (SNR), Signal-to-Interference-plus-Noise Ratio
(SINR), velocity of the mobile station 14, Bit Error Rate (BER), Received
Strength of Signal Indicator (RSSI), Channel Quality Indicator (CQI), or
the like. The transmit channel may be a downlink transmit channel from
the base station 12 to the mobile station 14 or an uplink transmit
channel from the mobile station 14 to the base station 12. If the
transmit channel is a downlink channel, the one or more channel
conditions are measured by the mobile station 14 and returned to the base
station 12. If the transmit channel is an uplink channel, the base
station 12 measures the one or more channel conditions.

[0030] Based on the one or more channel conditions for the transmit
channel, the adaptive BLER function 20 determines a set of target BLERs
and, in some embodiments, a target transmission iteration for the
HARQ-enabled transmission and provides the same to the link adaptation
function 22. The target transmission iteration is the transmission
iteration for the HARQ-enabled transmission that is targeted for
successful decoding by the receiver. The adaptive BLER function 20
determines the set of target BLERs and, in some embodiments, the target
transmission iteration that will provide improved throughput for the one
or more channel conditions for the transmit channel. In one embodiment,
the set of target BLERs and, in some embodiments, the target transmission
iteration maximize throughput for the one or more channel conditions for
the transmit channel. In another embodiment, the set of target BLERs and,
in some embodiments, the target transmission iteration optimize
throughput and one or more additional parameters for the one or more
channel conditions for the transmit channel. The one or more additional
parameters may include, for example, latency, QoS, or the like.

[0031] More specifically, the set of target BLERs target an N-th
transmission iteration (i.e., the target transmission iteration) for
successful decoding by the receiver. Particularly for poor or moderate
channel conditions, N is greater than or equal to 2 such that an N-1th
retransmission for the HARQ-enabled transmission is targeted for
successful decoding by the receiver. As a result of targeting the N-th
transmission iteration (i.e., the N-1th retransmission), a higher, or
more aggressive, MCS(s) is(are) used for the transmission iterations for
the HARQ-enabled transmission than would have otherwise been used if
targeting the first transmission iteration (e.g., using a static 10%
target BLER regardless of channel conditions). The target BLERs are
selected such that the net effect of the more aggressive MCS(s) and HARQ
retransmission iteration(s) is improved throughput.

[0032] Preferably, the set of target BLERs includes separate target BLERs
for the transmission iterations for the HARQ-enabled transmission up to
at least the target transmission iteration for successful decoding of the
transmitted block of data by the receiver. For instance, if the target
transmission iteration is the 3rd transmission iteration (i.e., the
2nd retransmission), then the set of target BLERs includes a first
target BLER for the first transmission iteration, a second target BLER
for the second transmission iteration, and a third target BLER for the
third transmission iteration. The target BLER for the first transmission
is greater than or equal to the target BLER for the second transmission
iteration, the target BLER for the second transmission iteration is
greater than or equal to the target BLER for the third transmission
iteration, etc. For example, if the target transmission iteration is the
third transmission iteration, the set of target BLERs may be 90%, 90%,
10%. The target transmission iteration is the N-th transmission iteration
(i.e., the N-1th retransmission) for the HARQ-enabled transmission. At
least under some channel conditions (e.g., channel conditions near the
cell edge), N≧2. For instance, N may be greater than or equal to 2
for poor to moderate channel conditions (e.g., low to moderate SNR) and
equal to 1 for good channel conditions (e.g., high SNR).

[0033] In one embodiment, the adaptive BLER function 20 is implemented as
a Look Up Table (LUT) that is preconfigured with sets of target BLERs
and, in some embodiments, target transmission iterations for a number of
different channel conditions (e.g., two or more SNR ranges). The LUT may
be configured based on simulations, actual measurements of throughput
versus channel conditions for different target BLERs, or the like, or any
combination thereof. Using the one or more channel conditions for the
transmit channel as an input, the LUT outputs the corresponding set of
target BLERs and, in some embodiments, target transmission iteration. In
another embodiment, the adaptive BLER function 20 computes the set of
target BLERs and, in some embodiments, the target transmission iteration
based on the one or more channel conditions for the transmit channel
using a predetermined algorithm.

[0034] In this embodiment, the link adaptation function 22 includes an
inner loop link adaptation function 28 (hereinafter "inner loop 28") and
an outer loop link adaptation function 30 (hereinafter "outer loop 30").
In operation, prior to the first transmission iteration for the
HARQ-enabled transmission, the inner loop 28 determines or otherwise
selects an MCS for the first transmission iteration using any suitable
link adaptation algorithm. Notably, in some embodiments, the inner loop
28 may utilize the target transmission iteration as an input for the link
adaptation algorithm. The inner loop 28 provides the selected MCS to the
outer loop 30. Based on the target BLER for the first transmission
iteration from the set of target BLERs and a measured BLER (e.g., a
time-averaged actual BLER), the outer loop 30 adjusts the MCS for the
first transmission iteration using any suitable outer loop link
adaptation algorithm. In general, the outer loop 30 increases the MCS
(i.e., changes the MCS to a more aggressive MCS) and returns the adjusted
MCS to the inner loop 28. The inner loop 28 then outputs the adjusted MCS
and, in some embodiments, other transport parameters (e.g., transport
block size) to be used for the first transmission iteration.

[0035] Assuming that the first transmission iteration was not successful,
in one embodiment, the link adaptation function 22 determines an MCS for
the second transmission iteration (i.e., the first retransmission) for
the HARQ-enabled transmission. The outer loop 30 then adjusts the MCS for
the second transmission iteration based on the target BLER for the second
transmission iteration from the set of target BLERs for the HARQ-enabled
transmission and the measured BLER. Notably, in this embodiment, the set
of target BLERs is determined only once prior to the first transmission
iteration and is not updated during the HARQ-enabled transmission. The
adjusted MCS for the second transmission iteration is returned to the
inner loop 28 and then output for use for the second transmission
iteration. This process is repeated for any additional transmission
iterations until either the transmitted block of data has been
successfully decoded by the receiver or until a preconfigured maximum
allowable number of transmission iterations have been performed.

[0036] In another embodiment, assuming that the first transmission
iteration was not successful, the adaptive BLER function 20 obtains one
or more new channel conditions for the transmit channel (i.e., obtains
updates for the one or more channel conditions) prior to the second
transmission iteration. Based on the one or more new channel conditions,
the adaptive BLER function 20 determines a new set of target BLERs and,
in some embodiments, a new target transmission iteration for the
HARQ-enabled transmission. The inner loop 28 determines an MCS for the
second transmission iteration, and then the outer loop 30 adjusts the MCS
for the second transmission iteration based on a target BLER for the
second transmission iteration from the new set of target BLERs. The
adjusted MCS is returned to the inner loop 28 and used for the second
transmission iteration. This process is repeated for any additional
transmission iterations until either the transmitted block of data has
been successfully decoded by the receiver or until a preconfigured
maximum allowable number of transmission iterations have been performed.

[0037] Before proceeding, it should be noted that while the discussion
herein focuses on adjusting MCS based on the target BLER, the present
disclosure is not limited thereto. In another embodiment, the set of
target BLERs are utilized to indirectly adjust the MCS. For example, in
one alternative embodiment, the set of target BLERs are utilized to
adjust gain values for the corresponding transmission iterations, which
in turn is directly or indirectly used to determine the MCS for the
corresponding transmission iterations. In another alternative embodiment,
the set of target BLERs are utilized to adjust a parameter relating to a
value connoting signal strength and a value connoting channel condition
for the corresponding transmission iterations, which in turn is directly
or indirectly used to determine the MCSs for the corresponding
transmission iterations.

[0038] FIGS. 3A and 3B are flow charts illustrating the operation of the
adaptive BLER function 20 and the outer loop 30, respectively, to provide
improved throughput for a HARQ-enabled transmission according to one
embodiment of the present disclosure. As illustrated in FIG. 3A, the
adaptive BLER function 20 first obtains one or more channel conditions
for a transmit channel for the HARQ-enabled transmission prior to the
HARQ-enabled transmission (i.e., prior to a first transmission iteration
for the HARQ-enabled transmission) (step 100). Next, the adaptive BLER
function 20 determines a set of target BLERs that provides optimal
throughput utilizing HARQ retransmission based on the one or more channel
conditions (step 102). As discussed above, the optimal throughput may be
maximum throughput or an optimization of throughput and one or more
additional parameters. The adaptive BLER function 20 then outputs the set
of target BLERs to the outer loop 30 (step 104). In addition, as
discussed above, the adaptive BLER function 20 may output a target
transmission iteration to the inner loop 28 and/or the outer loop 30. In
this embodiment, the set of target BLERs and, if desired, the target
transmission iteration for the HARQ-enabled transmission are determined
only once for the HARQ-enabled transmission and are not updated during
the HARQ-enabled transmission.

[0039] As illustrated in FIG. 3B, the outer loop 30 obtains the set of
target BLERs from the adaptive BLER function 20 for the HARQ-enabled
transmission (step 200). The outer loop 30 also obtains an MCS selected
for the first transmission iteration from the inner loop 28 (step 202).
The outer loop 30 adjusts the MCS for the transmission iteration, which
at this point is the first transmission iteration, based on the
corresponding target BLER from the set of target BLERs (step 204). The
outer loop 30 then returns the adjusted MCS to the inner loop 28 (step
206). Next, a determination is made by the outer loop 30 as to whether a
HARQ retransmission is needed (step 208). A HARQ retransmission is needed
when a negative acknowledgement (NACK) or similar message is received
from the receiver indicating that the receiver did not decode the
transmitted block of data successfully. If no HARQ retransmission is
needed, the process ends because the HARQ-enabled transmission has
completed. However, if a HARQ retransmission is needed, the outer loop 30
obtains an MCS selected for the next transmission iteration from the
inner loop 28 (step 210). The process then returns to step 204 and is
repeated.

[0040] FIG. 4 is a flow chart illustrating the operation of the adaptive
BLER function 20 according to one alternative embodiment of the present
disclosure. The adaptive BLER function 20 first obtains one or more
channel conditions for a transmit channel for the HARQ-enabled
transmission prior to the HARQ-enabled transmission (i.e., prior to a
first transmission iteration for the HARQ-enabled transmission) (step
300). Next, the adaptive BLER function 20 determines whether the
HARQ-enabled transmission is time sensitive (step 302). If the
HARQ-enabled transmission is not time-sensitive, the adaptive BLER
function 20 determines a set of target BLERs that provides optimal
throughput utilizing HARQ retransmission based on the one or more channel
conditions (step 304). As discussed above, the optimal throughput may be
maximum throughput or an optimization of throughput and one or more
additional parameters. The adaptive BLER function 20 then outputs the set
of target BLERs to the outer loop 30 (step 306), where the set of target
BLERs is utilized as discussed above with respect to FIG. 3B. In
addition, as discussed above, the adaptive BLER function 20 may output a
target transmission iteration to the inner loop 28 and/or the outer loop
30. In this embodiment, the set of target BLERs and, if desired, the
target transmission iteration for the HARQ-enabled transmission are
determined only once for the HARQ-enabled transmission and are not
updated during the HARQ-enabled transmission.

[0041] Returning to step 302, if the HARQ-enabled transmission is time
sensitive, the adaptive BLER function 20 determines a set of target BLERs
that provides optimal latency based on the one or more channel conditions
(step 308). Then, as discussed above, the adaptive BLER function 20
outputs the set of target BLERs to the outer loop 30 (step 306), where
the set of target BLERs is utilized as discussed above with respect to
FIG. 3B. In addition, as discussed above, the adaptive BLER function 20
may output a target transmission iteration to the inner loop 28 and/or
the outer loop 30. In this embodiment, the set of target BLERs and, if
desired, the target transmission iteration for the HARQ-enabled
transmission are determined only once for the HARQ-enabled transmission
and are not updated during the HARQ-enabled transmission.

[0042] FIGS. 5A and 5B are flow charts illustrating the operation of the
adaptive BLER function 20 and the outer loop 30, respectively, to provide
improved throughput for a HARQ-enabled transmission according to one
embodiment of the present disclosure. As illustrated in FIG. 5A, the
adaptive BLER function 20 first obtains one or more channel conditions
for a transmit channel for the HARQ-enabled transmission prior to the
HARQ-enabled transmission (i.e., prior to a first transmission iteration
for the HARQ-enabled transmission) (step 400). Next, the adaptive BLER
function 20 determines a set of target BLERs that provides optimal
throughput utilizing HARQ retransmission based on the one or more channel
conditions (step 402). As discussed above, the optimal throughput may be
maximum throughput or an optimization of throughput and one or more
additional parameters. The adaptive BLER function 20 then outputs the set
of target BLERs to the outer loop 30 (step 404). In addition, as
discussed above, the adaptive BLER function 20 may output a target
transmission iteration to the inner loop 28 and/or the outer loop 30.
Next, a determination is made by the adaptive BLER function 20 as to
whether a HARQ retransmission is needed (step 406). A HARQ retransmission
is needed when a NACK or similar message is received from the receiver
indicating that the receiver did not decode the transmitted block of data
successfully. If no HARQ retransmission is needed, the process ends
because the HARQ-enabled transmission has completed. However, if a
HARQ-enabled retransmission is needed, the adaptive BLER function 20
obtains updated, or new, channel condition(s) prior to the next
transmission iteration for the HARQ transmission (step 408). The process
then returns to step 402 and is repeated.

[0043] As illustrated in FIG. 5B, prior to the first iteration for the
HARQ-enabled transmission, the outer loop 30 obtains the set of target
BLERs from the adaptive BLER function 20 for the HARQ-enabled
transmission (step 500). The outer loop 30 also obtains an MCS selected
for the first transmission iteration from the inner loop 28 (step 502).
The outer loop 30 adjusts the MCS for the transmission iteration, which
at this point is the first transmission iteration, based on the
corresponding target BLER from the set of target BLERs (step 504). The
outer loop 30 then returns the adjusted MCS to the inner loop 28 (step
506). Next, a determination is made by the outer loop 30 as to whether a
HARQ retransmission is needed (step 508). A HARQ retransmission is needed
when a NACK or similar message is received from the receiver indicating
that the receiver did not decode the transmitted block of data
successfully. If no HARQ transmission is needed, the process ends because
the HARQ-enabled transmission has completed. However, if a HARQ
retransmission is needed, the outer loop 30 obtains an updated, or new,
set of target BLERs for the HARQ-enabled transmission from the adaptive
BLER function 20 (step 510). As discussed above, the updated, or new, set
of target BLERs are determined by the adaptive BLER function 20 prior to
the next transmission iteration based on the updated channel condition(s)
for the transmit channel. In addition, the outer loop 30 obtains an MCS
selected for the next transmission iteration from the inner loop 28 (step
512). The process then returns to step 504 and is repeated.

[0044] FIG. 6 is a flow chart illustrating the operation of the adaptive
BLER function 20 according to one alternative embodiment of the present
disclosure. As illustrated in FIG. 6, the adaptive BLER function 20 first
obtains one or more channel conditions for a transmit channel for the
HARQ-enabled transmission prior to the HARQ-enabled transmission (i.e.,
prior to a first transmission iteration for the HARQ-enabled
transmission) (step 600). Next, the adaptive BLER function 20 determines
whether the HARQ-enabled transmission is time sensitive (step 602). If
the HARQ-enabled transmission is not time sensitive, the adaptive BLER
function 20 determines a set of target BLERs that provides optimal
throughput utilizing HARQ retransmission based on the one or more channel
conditions (step 604). As discussed above, the optimal throughput may be
maximum throughput or an optimization of throughput and one or more
additional parameters. The adaptive BLER function 20 then outputs the set
of target BLERs to the outer loop 30 (step 606), where the set of target
BLERs is utilized as discussed above with respect to FIG. 5B. In
addition, as discussed above, the adaptive BLER function 20 may output a
target transmission iteration to the inner loop 28 and/or the outer loop
30. Returning to step 602, if the HARQ-enabled transmission is time
sensitive, the adaptive BLER function 20 determines a set of target BLERs
that provide optimal latency based on the one or more channel conditions
(step 608). Then, as discussed above, the adaptive BLER function 20
outputs the set of target BLERs to the outer loop 30 (step 606), where
the set of target BLERs is utilized as discussed above with respect to
FIG. 5B.

[0045] Next, a determination is made by the adaptive BLER function 20 as
to whether a HARQ retransmission is needed (step 610). A HARQ
retransmission is needed when a NACK or similar message is received from
the receiver indicating that the receiver did not decode the transmitted
block of data successfully. If no HARQ retransmission is needed, the
process ends because the HARQ-enabled transmission has completed.
However, if a HARQ retransmission is needed, the adaptive BLER function
20 obtains updated, or new, channel condition(s) prior to the next
transmission iteration for the HARQ-enabled transmission (step 612). The
process then returns to step 602 and is repeated.

[0046] FIGS. 7 through 9 graphically depict results of exemplary
simulations that illustrate throughput is improved by utilizing HARQ
retransmission in the manner described herein. More specifically, FIG. 7
illustrates exemplary simulation results for throughput versus SNR for an
exemplary LTE uplink channel (i.e., LTE uplink, Frequency Division
Duplexing (FDD), for EVA 70 hertz (Hz), low correlation, 10 megahertz
(MHz) bandwidth with 48 RBs for shared channel) for three scenarios,
namely: (1) a fixed MCS using a conventional low, static target BLER of
10%, (2) the same fixed MCS without HARQ, and (3) the same fixed MCS with
HARQ. These simulation results show that there is room for improving
throughput by using HARQ retransmission. In other words, using a static
target BLER of 10% does not use the full capacity of the HARQ feature.

[0047] FIG. 8 illustrates the same exemplary simulation results from FIG.
7 with the addition of simulation results for a static BLER of 90%. These
simulation results show that, if the target BLER is increased to, for
example, 90%, the throughput of the curve with link adaptation is
increased, particularly for low and moderate SNRs.

[0048]FIG. 9 illustrates the same exemplary simulation results from FIG.
8 with the addition of simulation results for an exemplary implementation
of an embodiment of the adaptive target BLER process described herein. As
illustrated, the adaptive target BLER process results in optimal
throughput for all channel conditions.

[0049] FIGS. 10 and 11 illustrate results of exemplary simulations for
throughput versus target BLER for low SNRs (e.g., SNRs encountered for
cell-edge mobile stations) and moderate SNRs, respectively. As
illustrated, for each SNR value, there is an optimal target BLER that
provides the optimal throughput. In this example, the optimal throughput
is the maximum throughput. Note, however, that other parameters (e.g.,
latency) may be taken into consideration in additional to throughput in
which case the optimal throughput may be a throughput near but not
necessarily equal to the maximum throughput. For example, for an SNR of 0
decibels (dB), while the maximum throughput is achieved for a target BLER
of 60%, a target BLER of, for example, 50% or 70% may optimize both
throughput and one or more additional parameters. From FIGS. 10 and 11,
it can be seen that throughput may be optimized by using high target
BLERs for low SNRs and moderate target BLERs for moderate SNRs.

[0050] FIGS. 12 through 15 are exemplary simulation results that
illustrate that throughput can be optimized by targeting different
transmission iterations based on channel conditions. More specifically,
FIG. 12 illustrates normalized throughput versus normalized SNR for a
typical FMC curve with fixed MCS=M. In general, at a normalized SNR of 1,
a HARQ-enabled transmission is always successfully received on the first
transmission iteration, in which case maximum throughput is achieved. In
this example, as the normalized SNR decreases from 1 to a value just
above 0.9, the HARQ-enabled transmission is sometimes successfully
received on the first transmission iteration and sometimes successfully
received on the second transmission iteration, in which case throughput
begins to decrease. In this example, as the normalized SNR continues to
decrease from just above 0.9 to about 0.75, the HARQ-enabled transmission
is always successfully received on the second transmission iteration. As
the normalized SNR further decreases, the HARQ-enabled transmission is
sometimes successfully received on the second transmission iteration and
sometimes successfully received on the third transmission iteration. The
pattern continues until the normalized SNR reaches a point where the
HARQ-enabled transmission is never successfully received in the maximum
allowed number of transmission iterations, which in this example is 8.

[0051]FIG. 13 illustrates curves similar to that of FIG. 12 but for
multiple different MCSs (M, M-1, M-2, etc.), where M is the most
aggressive MCS, M-1 is the next most aggressive MCS, etc. As shown, for
each normalized SNR value, there is a corresponding MCS that provides
optimal throughput.

[0052] FIG. 14 illustrates exemplary simulations for throughput versus SNR
for link adaptation algorithms, when adaptive MCS is allowed, with fixed
HARQ transmission number and BLER termination targets. FIG. 14 shows that
for each SNR value, throughput can be optimized by targeting
corresponding transmission iteration. For example, in FIG. 14, targeting
the second transmission iteration provides optimal throughput for
normalized SNR values in the range of about 0.29 to 0.45.

[0053] FIG. 15 uses the curves for the fixed HARQ termination numbers from
FIG. 14 to illustrate an adaptive target transmission iteration scheme
that optimizes throughput. In this example, throughput is optimized by
targeting the first transmission iteration for normalized SNRs above
about 0.45, targeting the second transmission iteration for normalized
SNRs in the range of about 0.29 to 0.45, targeting the third transmission
iteration for normalized SNRs in the range of about 0.18 to 0.29, and so
on. As discussed above, the adaptive BLER function 20 controls the target
BLER to effect target transmission iterations that optimize throughput.
FIG. 15 illustrates that adaptively controlling the target transmission
iteration improves throughput.

[0081] Those skilled in the art will recognize improvements and
modifications to the preferred embodiments of the present disclosure. All
such improvements and modifications are considered within the scope of
the concepts disclosed herein and the claims that follow.